Wear resistant sliding element having a low coefficient of friction

ABSTRACT

A sliding element according to the invention comprises from approximately 30 to approximately 80% of a graphite powder, from approximately 0.5 to 30% of lead-containing powder, and from 15 to 45% of an organic resin binder, all percentages being by weight based on the weight of the hot pressed body. Due to incorporation of both graphite carbon powder and lead-containing powder to the organic resin binder, the conformability, wear resistance and low friction properties of the sliding element are superior to those obtained by a single addition of the graphite carbon or lead powder alone.

The present invention relates to a sliding element, and particularly an improvement of a sliding element manufactured by hot pressing an organic resin binder and either graphite powder or lead-containing powder. The term "sliding" used herein means relative movement of at least two sliding elements with friction between these elements, and the relative movement may be rotational, reciprocating or any other type movement.

It is known to blend in powder form a filler having a low coefficient of friction, such as lead, lead oxide, molybdenum disulphide, red oxide, sericite and zinc oxide, with an organic resin binder and to hot press the so blended mixture to form a sliding element. A hot pressed sliding unit has been used for various sliding contacts, in which an iron based stationary sliding element and the hot pressed sliding element are slidably brought into contact with one another. Conventionally, either lead containing powder i.e. lead powder or lead oxide powder, or graphite powder have been blended in a organic resin binder and, then, hot pressed. Previously no attempts have been made to incorporate both graphite powder and lead-containing powder into the organic resin binder, because the improvement of the sliding element by incorporation of both of the powders mentioned above could not be anticipated from the prior art.

The present inventors discovered that a sliding element containing either lead containing powder or graphite powder is not satisfactory, because the sliding element is not highly resistant to wear, and further, because a stable, tight sliding contact cannot readily be provided between the surfaces of face materials.

The present inventors also discovered that, when both graphite powder and lead containing powder are incorporated into an organic resin binder, the sliding characteristics of the sliding element can be considerably improved over those of the conventional sliding element.

It is an object of the present invention to provide a sliding element having improved sliding characterstics over those of the sliding element containing either lead-containing powder or graphite powder.

It is another object of the present invention to improve the sliding characteristics of the sliding contacts between the hot pressed sliding element and the iron based stationary sliding element, mentioned above, over the sliding characteristics of the sliding contacts in which the hot pressed sliding element contains either graphite powder or lead containing powder.

In accordance with the objects of the present invention, there is provided a sliding element comprising a hot pressed body, said hot pressed body comprising from approximately 30 to 80% of graphite powder, from approximately 0.5 to 30% of lead-containing powder, and from approximately 15 to approximately 45% of an organic resin binder, all percentages being by weight based on the weight of the hot pressed body. The components of the hot pressed body will now be explained in detail. First, the graphite powder and the graphite carbon powder are distinguished from a carbonaceous carbon powder, in that the carbonaceous carbon powder is a carbon which is not graphitized and is, therefore, amorphous. The graphite carbon powder has a property intermediate between the carbonaceous carbon powder and the graphite powder. The graphite carbon powder and the graphite powder, which powders are collectively referred to herein as graphite powder, can be used in the present invention. The graphite powder may be mainly composed of graphitized carbon or of amorphous carbon. In addition, the graphite powder may be composed of a completely graphitized carbon or of a not completely crystallized or graphitized carbon. The grahite powder possesses a grain size of preferably 300 microns or less, more preferably from 10 to 100 microns. When the percentage of the graphite powder in the sliding element is less than approximately 30%, the sliding characteristics of the sliding element are deteriorated from those containing 30% or more of the graphite powder. When the percentage of graphite powder is more than approximately 80%, the hardness of the sliding element tends to be low. The percentage of the graphite powder is preferably from 40 to 70%. Furthermore, the graphite powder is preferably irregularly shaped.

Second, the lead-containing powder may be composed of lead, or a lead alloy, and may contain a minor amount of lead oxide, which is formed on the powder surface. Such a powder is hereinafter referred to as a lead powder. The grain size of the lead-containing powder should be 200 microns or less and preferably from 10 to 60 microns. When the percentage of the lead-containing powder in the sliding element is less than approximately 0.5%, the conformability due to the lead cannot be improved appreciably over that of the conventional sliding element. The conformability involves various technical concepts, but can usually be considered as a property of a quickly stabilized frictional contact between the face materials, particularly of different kinds. On the other hand, when the percentage of the lead-containing powder is more than approximately 30%, the strength of the sliding element is too low to provide the sliding element with a satisfactorily high wear resistance. The percentage of the lead-containing powder is preferably from 0.5 to 10%. Furthermore, the lead powder is preferably irregularly shaped, such as seen in a crushed lead powder.

Due to addition of both graphite powder and lead-containing powder to the organic resin binder, the conformability, wear resistance and low friction properties of the sliding element are superior to those obtained by addition of the graphite or lead-containing powder alone.

Third, the organic resin binder may be a resin having excellent toughness and rigidity as well as strong adhesion, such as a phenol resin, an epoxy resin or a furan resin. The organic resin binder may include lead stearate as a die lubricant in an appropriate amount, for example 1%, in addition to the resin. An inclusion of a trace amount of a soft material, such as cadmium and indium, in the organic resin binder is allowable. The percentage of organic resin binder should be from approximately 15 to approximately 45%. When the percentage of the organic resin binder is less than approximately 15%, the strength of the sliding element is too low to provide the sliding element with a satisfactorily high wear resistance. When the percentage of the organic resin binder is more than approximately 45%, the sliding characteristics of the sliding element are deteriorated from those of the sliding element containing approximately 45% or less of the organic resin binder. The percentage of the organic resin binder is preferably from approximately 25 to approximately 40%.

The present invention will be further explained with reference to the drawings, wherein:

FIGS. 1 and 2 are schematic views of several sliding contacts between the sliding element of the present invention and a face material, and;

FIGS. 3 and 4 are graphs of coefficients of friction.

The sliding element according to the present invention is suitable for use as a sliding element which is rotatable with respect to a stationary element of a sliding unit under a high pressure, for example, a thrust force, of for example up to 30 kg/cm² under dry friction condition.

The sliding element according to the present invention may have a structure as illustrated in FIGS. 1 and 2. The cylindrical sliding element 51 according to the present invention may be rotated around the central axis of a stationary hollow disc 52 consisting of a face material under a thrust force. The most severe sliding conditions under which the sliding element 51 can reliably be used are as follows.

A. Thrust pressure: 30 kg/cm² at the maximum.

B. Ambient temperature: 25° C.

C. Sliding speed: 20 m/sec at the maximum.

D. Friction condition: dry friction (without lubricant)

E. Face material: Nodular cast iron.

The sliding element 51 according to the present invention may be reciprocated or rotated in a stationary hollow disc 52 of face material as illustrated in FIG. 2. The sliding movement as illustrated in FIG. 2 occurs under less severe conditions than in FIG. 1. It is possible according to the present invention to provide a tight sliding contact between the rotatable and stationary elements mentioned above. When the grain size of the graphite powder and lead-containing powder is from 10 to 60 microns, the sliding contact mentioned above is particularly tight for a long period of time.

In an embodiment of the present invention, the sliding element further comprises at least one member selected from the group consisting of a silicon dioxide powder and a silicate powder, in an amount of from approximately 2 to approximately 15%. The silicon dioxide includes quartz and the silicate includes sericite and talc. The grain size of the silicon dioxide and silicate powders should be 50 microns or less and preferably in the range of from 5 to 25 microns. In the sliding element of the embodiment mentioned above, the percentage of graphite powder is from approximately 40 to approximately 70%, the percentage of lead-containing powder is from approximately 0.5 to approximately 30%, and the percentage of organic resin binder is from approximately 25 to approximately 40%. The sliding element containing an additive ingredient of the silicon dioxide and/or silicate powders is further improved over that containing only the three ingredients mentioned above, in the points of the coefficient of friction, and the conformability and wear resistant properties. The functions of the additive ingredients of silicon dioxide and silicate will now be explained. These additive ingredients are capable of preventing an adhesion between the face materials. In this regard, the lead-containing powder and graphite powder, which are incorporated into the organic resin binder, are liable to generate the adhesion mentioned above. When the total percentage of the additive ingredient is less than approximately 2.5%, effective prevention of the adhesion cannot be expected. When the percentage of the additive ingredient is more than approximately 20%, the surface of the sliding element becomes rough, with the result that the mating face material is quickly worn out by the sliding element. The percentage of additive ingredient is preferably from 5 to 20%.

In another embodiment of the present invention, the sliding element comprises from approximately 0.5 to approximately 15% of boron nitride powder, in addition to from approximately 30 to approximately 80% of graphite powder, from approximately 0.5 to approximately 30% of the lead-containing powder, and from approximately 15 to approximately 45% of the organic resin binder. The grain size of the boron nitride powder should be 60 microns or less and preferably from 10 to 30 microns. The sliding element containing the boron nitride powder is further improved over that containing the lead-containing powder and graphite powder and the organic resin binder in the points of the coefficient of friction, and the conformability and wear resistant properties. The boron nitride powder is a hard solid lubricant and can provide the sliding element with a high wear resistance and low coefficient of friction when incorporated in the sliding element. When the percentage of the boron nitride powder is less than approximately 0.5%, it is difficult to effectively improve the high wear resistance and low friction property. On the other hand, when the percentage of boron nitride powder is more than approximately 15%, the mating face material tends to be quickly worn out by the boron nitride powder incorporated in the sliding element. The percentage of boron nitride powder is preferably from approximately 0.5 to 5%.

In a further embodiment of the present invention, the sliding element further comprises: at least one member selected from the group consisting of a silicon dioxide powder and a silicate powder, in an amount of from approximately 2 to approximately 15%, preferably from 5 to 10%, and; a boron nitride powder in an amount of from approximately 0.5 to approximately 15%, preferably from 0.5 to 5%. In this embodiment, the total percentage of the at least one member and the boron nitride powder is preferably from approximately 2.5 to approximately 20%. When such total percentage falls within the range of from approximately 2.5 to approximately 20% the coefficient of friction of the sliding element, which is dependent upon the face material to be brought into frictional contact with the sliding element, is generally low. Such face material is hereinafter referred to as a mating face material. It is preferable that the percentage of the silicate powder based on the total weight percentage of the silicon dioxide, silicate and boron nitride powders be not more than approximately 80%. When the total weight percentage exceeds approximately 80%, the coefficient of friction and the relative wear amount explained hereinbelow are larger than those of the sliding element in which such percentage is approximately 80% or less.

The present invention will now be explained in further detail by way of the following examples.

EXAMPLE 1

In the present Example, nineteen samples containing the ingredients as shown in Table 1 were prepared by blending the ingredients, hot pressing the blended ingredients at a pressure of 350 kg/cm² and a temperature of 170° C., over a period of 3 minutes, and finally, curing the organic resin binder (phenol resin) of the hot pressed body at approximately 190° C., over a period of twelve hours. Among the so prepared samples, sample Nos. 18 and 19 were control sample containing one of the graphite powder and lead powder. The property of the ingredients used will now be explained. The graphite powder contained 60% of graphites and had a grain size of from 10 to 100 microns. The lead powder had grain size ranging from 10 to 100 microns. The lead powder was a commercially available crushed powder. The silicon dioxide powder was a quartz powder having grain size ranging from 5 to 25 microns. The boron nitride powder has a grain size ranging from 10 to 30 microns.

The prepared samples were subjected to a test by which the sliding characteristics were measured under the following conditions.

    ______________________________________                                         Mating Face Material                                                           Material         Equivalent to cast iron                                                        FC20 shaped into a hollow                                                      disc                                                          Surface roughness                                                                               1 micron (μm) at the                                                        maximum                                                       Sliding speed    2 m/sec.                                                      Dimension        Inner diameter of hollow                                                       part of 16 mm, outer                                                           diameter of the disc of                                                        30 mm and thickness 8 mm                                      Samples                                                                        Shape            Cylindrical shape                                             Dimension        Inner diameter of                                                              19 mm, outer diameter                                                          of 23 mm, and thickness of                                                     4 mm                                                          Surface roughness                                                                               1 micron (μm) at the                                                        maximum                                                       Load             20 kg/cm.sup.2 (no lubricant                                                   is used)                                                      Atmosphere       air at 25° C.                                          Testing time period                                                                             3 hours                                                       ______________________________________                                    

The result of the measurements is illustrated in the following Table 1.

                                      TABLE 1                                      __________________________________________________________________________                  Silicon                                                                             Boron         Heated Relative                                Sample                                                                              Graphite                                                                            Lead                                                                              Dioxide                                                                             Nitride Coefficient                                                                          Temperature                                                                           Wear Amount                             No.  (%)  (%)                                                                               (%)  (%) Resin                                                                              of Friction                                                                          (°C.)                                                                          (ml/m . kg × 10.sup.-5)           __________________________________________________________________________      1   80   3  --   --  bal 0.10-0.15                                                                            100-120                                                                               4.6                                      2   50   25 --   --  "   0.09-0.12                                                                             98-110                                                                               4.0                                      3   57   0.8                                                                               15   --  "   0.09-0.10                                                                            90-95  1.8                                      4   65   3  2    --  "   0.08-0.11                                                                             85-100                                                                               2.0                                      5   57   3  10   --  "   0.08-0.09                                                                            76-85  1.4                                      6   30   30 5    --  "   0.07-0.10                                                                            75-90  1.7                                      7   57   0.8                                                                               --   15  "   0.08-0.12                                                                             80-100                                                                               2.5                                      8   65   3  --   2   "   0.07-0.12                                                                             80-105                                                                               2.3                                      9   57   3  --   5   "   0.06-0.11                                                                             76-102                                                                               2.1                                     10   45   25 --   5   "   0.06-0.15                                                                             77-110                                                                               1.9                                     11   57   0.8                                                                               8    2   "   0.07-0.09                                                                            75-85  1.2                                     12   57   0.8                                                                               2    8   "   0.06-0.09                                                                            72-82  1.5                                     13   57   3  8    2   "   0.04-0.05                                                                            68-72  0.7                                     14   57   3  2    8   "   0.05-0.08                                                                            70-80  0.7                                     15   65   5  2    1   "   0.06-0.09                                                                            75-85  1.3                                     16   50   10 8    2   "   0.05-0.06                                                                            70-76  1.0                                     17   50   15 5    1   "   0.05-0.07                                                                            72-78  0.9                                     18   65   -- --   --  "   0.16-0.21                                                                            120-135                                                                               22.0                                    (control)                                                                      19   --   10 --   --  "   0.15-0.20                                                                            110-130                                                                               16.2                                    (Control)                                                                      __________________________________________________________________________

In Table 1, the term "Heated Temperature" means the temperature of the samples heated due to the friction between the samples and the mating face material. In addition, the term "Relative Wear Amount" means volume of worn out material per product of load and friction length. As is clear from Table 1, the coefficient of friction, heated temperature and relative wear amount of Samples Nos. 1 and 2, containing both graphite and lead powders, are lower than those of Samples Nos. 18 and 19, containing the graphite or lead powder alone. This fact demonstrates that the frictional and wear resistant properties of the sliding element containing both the lead and graphite powders are superior to those containing only one of these powders. It is also clear from Table 1, that the frictional and wear resistant properties are further enhanced by blending the lead and graphite powders with: silicon dioxide powder (Samples Nos. 3 through 6); boron nitride powder (Samples Nos. 7 through 10), and; both silicon dioxide and boron nitride powders (Samples Nos. 11 through 17).

FIG. 3 illustrates the change of the coefficient of friction of Samples Nos. 1, 5, 9, 13, 18 and 19 during a testing period of three hours. As seen in FIG. 3, the coefficient of friction is reduced after a certain testing period to a low stabilized value. However, in Samples Nos. 18 and 19 the time required for the stabilization of the coefficient of friction is longer than in Samples Nos. 1, 5, 9 and 13. This fact demonstrates that the conformability of the sliding element according to the present invention is superior to that of the conventional sliding element.

In addition to the measurement mentioned above, measurements of the hardness and traverse bending strength of Samples of the present invention were conducted. The shore hardness was in the range of from Hs 85 to 95 and the traverse bending strength was in the range of from 7.5 to 8.5 kg/cm².

EXAMPLE 2

The procedure of Example 1 was repeated, except that instead of the phenol resin, epoxy resin, furan resin and polyimide resin were used as the organic resin binder, and further, the measurements of hardness and traverse bending strength were not carried out.

The percentage of the ingredients and the properties of the produced Samples are illustrated in Table 2.

                                      TABLE 2                                      __________________________________________________________________________                 Silicon                                                                             Boron                       Heated Relative                   Sample                                                                             Graphite                                                                            Lead                                                                              Dioxide                                                                             Nitride                                                                            Organic Resin     Coefficient                                                                          Temperature                                                                           Wear Amount                No. (%)  (%)                                                                               (%)  (%) phenol                                                                             Epoxy                                                                              Furan                                                                              Polyimide                                                                            of Friction                                                                          (°C.)                                                                          (ml/m . kg ×                                                             10.sup.-5)                 __________________________________________________________________________      1  80   3  --   --  bal --  --  --    0.10-0.15                                                                            100-120                                                                               4.6                         5  57   3  10   --  bal --  --  --    0.08-0.09                                                                            76-85  1.4                         9  57   3  --   5   bal --  --  --    0.06-0.11                                                                             76-102                                                                               2.1                        13  57   3   8   2   bal --  --  --    0.04-0.05                                                                            68-72  0.7                        20  80   3  --   --  --  --  --  bal   0.12-0.16                                                                            105-118                                                                               5.0                        21  57   3  10   --  --  bal --  --    0.10-0.14                                                                            100-120                                                                               6.2                        22  57   3  --   5   --  --  bal --    0.08-0.13                                                                             80-110                                                                               2.6                        23  57   3   8   2   --  --  --  bal   0.06-0.07                                                                            75-80  1.5                        __________________________________________________________________________

Each of the Samples Nos. 20 through 23 of the present Example had the same percentage of the ingredients including the organic resin binder, of Samples Nos. 1, 5, 9 and 13 of Example 1, respectively. It is clear from Table 2 that results similar to Example 1 were obtained in Example 2.

FIG. 4 is a similar graph to FIG. 3. It will be understood from FIG. 4 that the conformability of Samples Nos. 9 and 22, both containing the same percentage of the ingredients but different kinds of organic resin binders, display similar conformability property to one another.

EXAMPLE 3

The procedure of Example 1 was repeated, except that the grain size of the graphite powder was varied, and further, the hardness and traverse bending strength were not measured.

                                      TABLE 3                                      __________________________________________________________________________     Graphite                                                                       (grain size in mesh)                                                                              Silicon                                                                             Boron                                                                              Organic    Heated Relative                         Sample                                                                             -145 ˜ +350                                                                      -425                                                                               Lead                                                                              Dioxide                                                                             Nitride                                                                            Resin                                                                               Coefficient                                                                          Temperature                                                                           Wear Amount                      No. (%)     (%) (%)                                                                               (%)  (%) (Phenol)                                                                            of Friction                                                                          (°C.)                                                                          (ml/m . kg                                                                     × 10.sup.-5)               __________________________________________________________________________      1  55      25  3  --   --  bal  0.10-0.15                                                                            100-120                                                                               4.6                               5  40      17  3  10   --  "    0.08-0.09                                                                            76-85  1.4                               9  40      17  3  --   5   "    0.06-0.11                                                                             76-102                                                                               2.1                              13  40      17  3   8   2   "    0.04-0.05                                                                            68-72  0.7                              24  25      40  3  --   --  "    0.12-0.17                                                                            103-122                                                                               5.8                              25  15      42  3  10   --  "    0.09-0.10                                                                            77-89  1.8                              26  17      40  3  --   5   "    0.08-0.13                                                                             80-105                                                                               3.0                              27  17      40  3   8   2   "    0.06-0.08                                                                            70-78  1.4                              __________________________________________________________________________

It is clear from Table 3, that results of Samples 24, 25, 26 and 27 are similar to those of Samples 1, 5, 9 and 13 of Example 1. 

What we claim is:
 1. A sliding element comprising a hot pressed body, said hot pressed body comprising from approximately 30 to approximately 80% of a graphitepowder, from approximately 0.5 to approximately 30% of a lead-containing powder, and from approximately 15 to approximately 45% of an organic resin binder, and from approximately 2 to 15% of at least one member selected from the group consisting of a silicon dioxide powder and a silicate powder, all percentages being by weight based on the weight of said hot pressed body.
 2. A sliding element according to claim 1, wherein said hot pressed body comprises from 5 to 10% of said at least one member.
 3. A sliding element according to claim 1, wherein said silicon dioxide powder is a quartz powder.
 4. A sliding element according to claim 1, wherein said silicate powder is a sericite powder.
 5. A sliding element according to claim 1, wherein said silicate powder is a talc powder.
 6. A sliding element according to claim 1, wherein the grain size of said dioxide powder is 50 microns or less.
 7. A sliding element according to claim 1, wherein said hot pressed body comprises from approximately 0.5 to approximately 15% of a boron nitride powder.
 8. A sliding element according to claim 7, wherein said hot pressed body comprises from approximately 0.5 to 5% of the boron nitride powder.
 9. A sliding element according to claim 7, wherein the grain size of said boron nitride powder is 60 microns or less.
 10. A sliding element according to claim 1, wherein said hot pressed body comprises: at least one member selected from the group consisting of a silicon dioxide powder and a silicate powder, in an amount of from approximately 2 to approximately 15%, and; a boron nitride powder in an amount of from approximately 0.5 to approximately 15%.
 11. A sliding element according to claim 10, wherein said hot pressed body comprises from 5 to 10% of said at least one member and from 0.5 to 5% of said boron nitride powder.
 12. A sliding element according to claim 10, wherein the total percentage of said at least one member and said boron nitride is in the range of from approximately 2.5 to approximately 20%.
 13. A sliding element according to claim 12, wherein the percentage of the silicate powder based on the weight percentage of the silicon dioxide, silicate and boron nitride powder is not more than approximately 80%. 